Add Ruby 3.4 to the CI (closes #268).

Author: postmodern

.github/workflows/ruby.yml

@@ -12,6 +12,7 @@ jobs:
           - '3.1'
           - '3.2'
           - '3.3'
+          - '3.4'
           # - jruby
           - truffleruby
     name: Ruby ${{ matrix.ruby }}